In image display devices having a backlight such as liquid crystal display devices, by controlling the luminance of the backlight based on an input image, the power consumption of the backlight can be suppressed and the image quality of a displayed image can be improved. In particular, by dividing a screen into a plurality of areas and controlling, based on an input image in an area, the luminances of backlight light sources provided for the area, a further reduction in power consumption and a further improvement in image quality can be achieved. A method of driving a display panel while thus controlling the luminances of backlight light sources based on an input image in each area is hereinafter referred to as “area active drive”.
An image display device that performs area active drive uses, for example, LEDs (Light Emitting Diodes) of three RGB colors or white LEDs, as backlight light sources. For the luminances of LEDs provided for each area (luminances upon light emission), appropriate luminances are determined based on the highest value and mean value of the luminances of pixels in each area, etc. The determined luminances are provided to a backlight drive circuit as LED data. In addition, based on the LED data and an input image, display data (in the case of a liquid crystal display device, data for controlling the light transmittances of liquid crystals) is generated, and the display data is provided to a display panel drive circuit. In the case of a liquid crystal display device, the luminance of each pixel on a screen is the product of the luminance of light from a backlight and a light transmittance based on display data.
By driving the display panel drive circuit based on display data generated in the above-described manner, and driving the backlight drive circuit based on the above-described LED data, image display based on the input image is performed.
Note that in relation to inventions pertaining to this subject, the following prior art document is known. Japanese Patent Application Laid-Open No. 2002-99250 discloses an invention of a conventional image display device that includes an illumination luminance control unit that controls the luminance of illumination light for every plurality of regions based on an input image signal; and an image signal converting unit that converts the input image signal based on information of the luminances, thereby achieving an increase in dynamic range and a reduction in power consumption in image display.